Effect of the synthetic method and support porosity on the structure and performance of silica‐supported CuBr/pyridylmethanimine atom transfer radical polymerization catalysts. I. Catalyst preparation and characterization

Abstract

AbstractSilica‐supported CuBr/pyridylmethanimine (PMI) complexes that facilitate the atom transfer radical polymerization of methyl methacrylate have been prepared and characterized. Four different synthetic routes, including multistep‐grafting (M1), two‐step‐grafting (M2), one‐pot (M3), and preassembled‐complex (M4) methods, have been evaluated on three different silica supports (mesoporous SBA15 with 48‐ and 100‐Å pores and nonporous Cab‐O‐Sil EH5). The resulting solids have been characterized by a battery of techniques, including thermogravimetric analysis/differential scanning calorimetry, FT‐Raman spectroscopy, 13C and 29Si magic‐angle‐spinning and cross‐polarity/magic‐angle‐spinning spectroscopy, low‐temperature nitrogen physisorption, and elemental analysis. The combination of elemental analysis and spectroscopic results has indicated that a variety of different surface species likely exist for most catalysts, including copper species that are both monocoordinated and biscoordinated by PMI ligands, and PMI‐free copper bromide species interacting with the silica surface. M4 appears to give a material that has the smallest amount of the uncomplexed ligand (by FT‐Raman spectroscopy) and is, therefore, the most homogeneous. After M4, the metallation efficiency decreases in the order M2 ≥ M3 > M1, with M1 giving a material with a highly heterogeneous surface composition. The ligand loading on all the catalysts has been determined to be approximately 1 mmol/g of SiO2, with Cab‐O‐Sil‐supported materials giving much higher ligand densities because of its lower surface area. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1367–1383, 2004